Georeferencing in GIS

Yuji Murayama

Division of Spatial Information Science

Brandon M. Vista

Teaching Assistant

Georeferencing

Is process of associating data points with specific locations on the earth’s surface.

It encompasses the definition, the physical/geometric constructs and the tools required to describe the geometry and motions of objects near and on the Earth`s surface.

Why is there a need for georeferencing in GIS?

Maps are a common source of input data for a GIS.　 Often input maps will be in different projections, requiring transformation of one or all maps to make coordinates compatible.

GIS are used for projects of global or regional scales so consideration of the effect of the earth's curvature is necessary.

Monitor screens are analogous to a flat sheet of paper, and need transformations from the curved surface to the plane for displaying data.

International Terrestrial Reference System

Spatial Reference Surfaces and Datums

Latitude and Longtitude

Is the most comprehensive and powerful method of georeferencing

Metric, standard, stable, unique

Uses a well-defined and fixed reference frame

Based on the Earth’s rotation and center of mass, and the Greenwich Meridian

Latitude and Longitude

Latitude represents an angular distance along a meridian north or south from the equator.

Longitude is an angular distance of a point on the earth's surface east or west of an arbitrarily defined meridian, usually the Greenwich meridian (Greenwich, England).

A line of longitude running vertically from the north pole to the south pole, but unlike lines of longitude, meridians terminate at the poles.

The Prime Meridian, currently called the Greenwich Meridian, runs through Greenwich, England, was agreed in 1884 as being the central meridian from which all other meridians would be referenced to in order to calculate longitude.

Map Projection

Because the earth is three-dimensional, some method must be used to depict the map in two dimensions. Therefore such representations distort some parameter of the earth's surface, be it distance, area, shape, or direction

A map projection is a method of representing the earth's three-dimensional surface as a flat two-dimensional surface. This normally involves a mathematical model that transforms the locations of features on the earth's surface to locations on a two-dimensional surface.

Distortions

Any projection must distort the Earth in some way.　 Distortion properties are usually classified according to what is not distorted on the map as follows:

Conformal property: Angles between lines on the curved reference surface are identical to the angles between the images of these lines on the map; Shapes of small features are preserved: anywhere on the projection the distortion is the same in all directions

Equal area property: area enclosed by the lines in the map are preserved but shapes are distorted

Equidistant property: length of a particular lines in the map are preserved

Three classes of map projections (Tangent - normal projection)

Three classes of map projections (Secant – ormal projection)

Other Projections
　(Transverse and Oblique projections)

Cylindrical Projections

Conceptualized as the result of wrapping a cylinder of paper around the Earth

Example: Mercator Sinusoidal

Conic Projections

Conceptualized as the result of wrapping a cone of paper around the Earth

Example: Lambert Conformal Conic

Azimuthal Projection

Conceptualized as the result of projecting a spherical surface onto a plane

Example: Gnomonic

The Universal Transverse Mercator (UTM) Projection

Developed in 1947 by US army

A type of cylindrical projection but unlike the normal cylindrical projection, it is called Transverse Mercator because the cylinder is wrapped around the Poles, not on the Equator.

Currently, the WGS84 ellipsoid is used as the underlying model of the Earth in the UTM coordinate system.

Implemented as an internationally standard coordinate system

スライド17

Summary of Projection Properties

References

Longley, Paul et. al (2005).　 Geographic Information Systems and Science.　 2nd ed. England: John Wiley & Sons, Ltd.

de By, Royce A., et. al. (2001). Principles of Geographic Information System: An Introductory Textbook. Royce de By (ed). Netherlands: International Institute for Geoinformation Science and Earth Observation (ITC).

Thank you

Thank you for your attention!


	Yuji Murayama
	Division of Spatial Information Science

	Brandon M. Vista
	Teaching Assistant


	Is process of associating data points with specific locations on the earth’s surface.
	It encompasses the definition, the physical/geometric constructs and the tools required to describe the geometry and motions of objects near and on the Earth`s surface.


	Maps are a common source of input data for a GIS.　 Often input maps will be in different projections, requiring transformation of one or all maps to make coordinates compatible.
	GIS are used for projects of global or regional scales so consideration of the effect of the earth's curvature is necessary.
	Monitor screens are analogous to a flat sheet of paper, and need transformations from the curved surface to the plane for displaying data.


	Is the most comprehensive and powerful method of georeferencing
		Metric, standard, stable, unique
	Uses a well-defined and fixed reference frame
		Based on the Earth’s rotation and center of mass, and the Greenwich Meridian


	Latitude represents an angular distance along a meridian north or south from the equator.
	Longitude is an angular distance of a point on the earth's surface east or west of an arbitrarily defined meridian, usually the Greenwich meridian (Greenwich, England).
	A line of longitude running vertically from the north pole to the south pole, but unlike lines of longitude, meridians terminate at the poles.
	The Prime Meridian, currently called the Greenwich Meridian, runs through Greenwich, England, was agreed in 1884 as being the central meridian from which all other meridians would be referenced to in order to calculate longitude.


	Because the earth is three-dimensional, some method must be used to depict the map in two dimensions. Therefore such representations distort some parameter of the earth's surface, be it distance, area, shape, or direction
	A map projection is a method of representing the earth's three-dimensional surface as a flat two-dimensional surface. This normally involves a mathematical model that transforms the locations of features on the earth's surface to locations on a two-dimensional surface.


	Any projection must distort the Earth in some way.　 Distortion properties are usually classified according to what is not distorted on the map as follows:

		Conformal property: Angles between lines on the curved reference surface are identical to the angles between the images of these lines on the map; Shapes of small features are preserved: anywhere on the projection the distortion is the same in all directions

		Equal area property: area enclosed by the lines in the map are preserved but shapes are distorted

		Equidistant property: length of a particular lines in the map are preserved


	Conceptualized as the result of wrapping a cylinder of paper around the Earth
	Example: Mercator Sinusoidal


	Conceptualized as the result of wrapping a cone of paper around the Earth
	Example: Lambert Conformal Conic


	Conceptualized as the result of projecting a spherical surface onto a plane
	Example: Gnomonic


	Developed in 1947 by US army
	A type of cylindrical projection but unlike the normal cylindrical projection, it is called Transverse Mercator because the cylinder is wrapped around the Poles, not on the Equator.
	Currently, the WGS84 ellipsoid is used as the underlying model of the Earth in the UTM coordinate system.
	Implemented as an internationally standard coordinate system


	Longley, Paul et. al (2005).　 Geographic Information Systems and Science.　 2nd ed. England: John Wiley & Sons, Ltd.
	de By, Royce A., et. al. (2001). Principles of Geographic Information System: An Introductory Textbook. Royce de By (ed). Netherlands: International Institute for Geoinformation Science and Earth Observation (ITC).